Another thing to bear in mind is that if you get a "purple" shade of walnut, it will lose the bluish tint over time (say 1-2 years) in favor of the more common dark brown. Over a longer period, it will gradually lighten and tend toward yellow from red, although still brown. We had a nice marble topped walnut table in our home for a while that was 40-50 years old, and it looked markedly different than any stick of walnut in my lumber stack.
Nogol (Peruvian Walnut) is in the walnut family, and also lightens over time, a bit more quickly than black walnut. I commissioned a piece of relief carving in Nogol from an Ecuadoran carver a while back, and he polished it with black shoe polish (ack!) to make sure that it would keep the dark look. Aside from the lack of judgment on the polish, he did an amazing job. He had a pretty extensive set of carving tools made in Ecuador of German steel. When I pushed him on his source of the steel, he admitted that his favorite was the steel from the springs of old BMWs. I have a couple of the Ecuadoran chisels just to remind myself that great work does not require great tools as much as knowing how to use the ones you have. Where there's a will, there's a way. He is one of the very few people I know whose work is better than his tools.
If you are ever in Ecuador, stop at the carver's shop on the equator (not the tourist route) on the way from Quito to Cayambe and you may meet him. Then continue to north to San Antonio de Ibarra, where the square has a big selection of carving shops and galleries, including some impressively sized relief carvings. Yes, you can buy tools made with German steel there. On the way back stop at the market in Otavalo, then stay at the Puertolago resort in San Rafael de la Laguna for a day or three. One of the best working vacations I ever had